MLA Citation: Bloomfield, Louis A. "Question 442"
How Everything Works 16 Jan 2018. 16 Jan 2018 <http://howeverythingworks.org/print1.php?QNum=442>.
442. I thought that glass could move, that is supposed to be a check for antique glass (It has flowed downward). Does glass move over hundreds of years?
People used to think so. They thought that glass was simply a very, very viscous liquid. However, it now appears that something happens below the glass transition temperature that stops all flow. In effect, the viscosity goes to infinity. While it might be a liquid in principle, it simply doesn't flow, even in terms of geological time scales. Antique glasses have non-uniform thicknesses because of how they were made. The earlier techniques involved stretching blown glass and tended to make sheets with irregular thicknesses. Antique glass exhibits these irregularities.

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